The primary technique for sharpening the blade of a power lawn mower is to remove the blade from the machine and then to apply a file or grinding stone to sharpen the blade edge. This is a time consuming task and can result in the unbalancing of the blade by removing too much of the blade's material on one if its sides.
One approach in the prior art to reducing the labor involved in sharpening the blades on rotary power lawn mowers has been to mount the sharpening device on the body of the mower. U.S. Pat. No. 3,225,527 is an example. Although this mode is convenient to the operator, it results in excessive wear on the blade because of the inherent imprecision of this type of device. Stationary sharpening devices have also been tried in the prior art, requiring the mower to be brought to the sharpening station. U.S. Pat. No. 3,596,412 is an example. With the power of the mower's motor applied to the rotating blade, the blade is brought into contact with the grinding stone at the station. Although this form of device provides a more controlled application of the grinding stone to the blade and therefor a better quality sharpening operation, the operator is confronted with the inconvenience of taking the mower to the sharpener, instead of taking the sharpener to the mower. Furthermore, this fixed-base type of prior art sharpener typically has many moving parts requiring excessive maintenance. Portable sharpeners are also available in the prior art, which do not mount onto the mower. U.S. Pat. No. 4,285,169 is an example. However, this type device relies on the vacuum developed by the rotary mower's blade and is inherently imprecise in its operation.